Methods and Apparatus for Transmission Lines in Packages

ABSTRACT

Methods and apparatus for forming a semiconductor device package with a transmission line using a micro-bump layer are disclosed. The micro-bump layer may comprise micro-bumps and micro-bump lines, formed between a top device and a bottom device. A signal transmission line may be formed using a micro-bump line above a bottom device. A ground plane may be formed using a redistribution layer (RDL) within the bottom device, or using additional micro-bump lines. The RDL formed ground plane may comprise open slots. There may be RDLs at the bottom device and the top device above and below the micro-bump lines to form parts of the ground planes.

BACKGROUND

Electronics can be divided into a simple hierarchy consisting of devicessuch as integrated circuit (IC) chips, packages, printed circuit boards(PCB), and systems. The package is the interface between an IC chip anda PCB. IC dies are made from semiconductor materials such as silicon.Dies are then assembled into semiconductor packages such as quad flatpacks (QFP), pin grid arrays (PGA), ball grid arrays (BGA), threedimensional integrated circuits (3DIC), wafer level packages (WLP), orpackage on package (PoP) devices, using wire bonding (WB), tapeautomated bonding (TAB), or flip chip (FC) bumping assembly techniques.The packaged die is then attached either directly to a PCB or to anothersubstrate as the second level packaging.

3DIC technologies are known as vertical interconnect packagingtechnologies as they exploit the vertical dimension of the chip toreduce interconnect length and to achieve greater integrationefficiency. The techniques for 3DIC package include wire-bonding,micro-bumps, through-vias, and more. A silicon interposer can be used toform a 3DIC package, where the interposer provides die-to-dieinterconnections for dies mounted on the interposer. For example, twodies may be bonded above each other by face-to-face or face-to-backstacking, with the lower die being coupled to the interposer byconnectors such as micro-bumps. Alternatively, multiple dies may also bemounted in parallel above an interposer, and coupled to the interposerby connectors such as micro-bumps.

Semiconductor packages equipped with wireless data and communicationsystems comprise various RF (radio frequency) transmitting structures,which sometimes are built on chip or in-package. Electromagnetic RFwaves or signals are conveyed through the packages or devices byconductive structures referred to as transmission lines. Transmissionlines, as an example, may be used for interconnecting individualelectrical elements together in a Monolithic Microwave IntegratedCircuit (MMIC), and for interconnecting MMICs together within microwaveMulti Chip Modules (MCMs).

In general, a transmission line includes at least two electricconductors or lines wherein one of the lines forms a ground (alsoreferred to as “ground plane”) and the other forms a signal transmissionline. The signal transmission line is variously arranged and combinedwith one or more ground planes or ground lines to form different typesof conductive transmission lines such as microstrip, coplanar waveguide(CPW), grounded coplanar waveguide (GCPW) transmission lines to servevarious RF signal applications. The signal transmission lines and groundconductors or planes are generally supported by some type of insulatingsubstrate or material such as a dielectric.

As semiconductor technology continues to advance and chip package sizeshrinks, such as by employing 3DIC die stacking, the distance betweenmetal layers in the conductive CMOS (complementary metal-oxidesemiconductor) structure becomes smaller, leading to increasingly largercapacitance between the metal layers and reduced performance of RFdevices. In addition, designing and fabricating transmission lineson-chip in a single chip or die becomes increasingly difficult withshrinking die packages in advanced semiconductor manufacturingtechnology nodes like the 20 nm process. Methods and apparatus areneeded for designing and fabricating transmission lines with improvedperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1( a)-1(f) illustrate cross-sectional views and a top view ofmicrostrip transmission lines formed within a package using a micro-bumplayer, in accordance with some embodiments;

FIGS. 2( a)-2(e) illustrate cross-sectional views and a threedimensional view of coplanar waveguide (CPW) transmission lines formedwithin a package using a micro-bump layer, in accordance with someadditional embodiments; and

FIGS. 3( a)-3(d) illustrate cross-sectional views and a threedimensional view of grounded coplanar waveguide (GCPW) transmissionlines formed within a package using a micro-bump layer, in accordancewith some embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that theembodiments of the present disclosure provide many applicable conceptsthat can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed are merely illustrative of specific waysto make and use the disclosure, and do not limit the scope of thedisclosure.

As will be illustrated in the following, methods and apparatus forforming a semiconductor device package with transmission lines using amicro-bump layer are disclosed. The micro-bump layer may comprisemicro-bumps and micro-bump lines, formed between a top die and a bottomdie, or between a die and an interposer. A signal transmission line maybe formed using a micro-bump line above a device. A ground plane may beformed using a redistribution layer (RDL) within a device, or usingadditional micro-bump lines. The RDL formed ground plane may compriseopen slots. There may be RDLs at a bottom device and top device aboveand below the micro-bump lines to form parts of the ground planes.Transmission lines so formed have lower resistance, and save the areasoccupied by the transmission lines.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, or connected or coupled to the other element orlayer or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to” or “directly coupled to” another element or layer, thereare no intervening elements or layers present.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present inventive concept.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “above” or “below” can encompassboth an orientation of above and below. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent inventive concept. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,”—when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. It shouldbe appreciated that the following figures are not drawn to scale;rather, these figures are merely intended for illustration.

FIG. 1( a) illustrates a cross-sectional view of a microstriptransmission line formed within a package using a micro-bump layer, inaccordance with some embodiment. In general, a microstrip transmissionline comprises a signal transmission line made of a thin flat conductorand a ground plane, where the signal transmission line is in parallel tothe ground plane, separated from the ground plane by some type ofinsulating substrate or material such as a dielectric.

As illustrated in FIG. 1( a), a semiconductor device package 100comprising a transmission line 490 may be formed on a device 301. Thedevice 301 may comprise: a substrate 302 with through vias (TV) 303, adielectric layer 311, a plurality of contact pads 321, a passivationlayer 341, an insulator layer 361, a redistribution layer (RDL)comprising segments 480 and 489, another insulator layer 371, and anunder bump metal (UBM) layer comprising UBM pad 391 covering openings ofthe insulator layer 371, and UBM line 390 above the insulator layer 371in parallel to the RDL segment 480, or simply referred as RDL 480. Amicro-bump layer may be formed above the device 301. The micro-bumplayer comprises micro-bump line 470 on the UBM line 390 in parallel tothe RDL 480, and a micro-bump 485 placed on the UBM pad 391, which isfurther connected to the RDL 489 inside the device 301. A die 601 may beplaced above the device 301, connected to the micro-bump 485 byconnectors 603. An underfill 571 may fill the gap between the device 301and the die 601, covering the micro-bump line 470, the micro-bump 485,and connectors 603. Each of these structures is discussed in greaterdetail in the following paragraphs.

The RDL 480, the micro-bump line 470 separated from the RDL 480 by theinsulator layer 371, and the UBM line 390 under the micro-bump line 470form the transmission line 490, where the RDL 480 is the ground plane,and the micro-bump line 470 and the UBM line 390 form the signaltransmission line. In some alternative embodiments, the UBM line 390 maynot exist and the micro-bump line 470 alone is placed on the insulatorlayer 371 to act as the signal transmission line.

The device 301 may be an interposer comprising a substrate, with throughvias formed within the substrate, and a plurality of contact pads,passivation layers, insulator layers, RDLs, and a UBM layer.Alternatively, the device 301 may be a part of a chip or an integratedcircuit (IC) die, which may be a back or front side of a die. When thedevice 301 is a part of a die, the die 601 is placed on the IC device301, which will be further coupled to an interposer by connectors suchas micro-bumps to form a package such as a 3DIC package. In the casewhen the device 301 is a part of a die, it may be called as a bottomdie, and the die 601 may be called a top die. When the device 301 is theback of a die, then the package 100 is formed by face-to-back stackingof the dies 301 and 601. When the device 301 is the front side of a die,then the package 100 is formed by face-to-face stacking of the dies 301and 601. Alternatively, the device 301 may be a package substratewithout through vias, any or all of the layers described above. Thesedevices and any other suitable devices may alternatively be used and arefully intended to be included within the scope of the presentembodiments.

The substrate 302 for the device 301 may be, e.g., a silicon substrate,doped or undoped, or an active layer of a silicon-on-insulator (SOI)substrate, used to provide support for the device 301. However, thesubstrate 302 may alternatively be a glass substrate, a ceramicsubstrate, a polymer substrate, or any other substrate that may providea suitable protection and/or interconnection functionality. These andany other suitable materials may alternatively be used for the substrate302. There may be a plurality of active or passive components, such astransistors, capacitors, resistors, and the like, formed within thesubstrate 302, which are not shown in FIG. 1( a). As one of ordinaryskill in the art will recognize, a wide variety of active or passivecomponents may be used to generate the desired structural and functionalrequirements of the design for the device 301.

A plurality of TVs 303 may be formed through the substrate 302. The TVs303 may be formed by applying and developing a suitable photoresist, andthen etching the substrate 302 to generate TV openings. The openings forthe TVs 303 may be formed to extend into the substrate 302 to a depth atleast greater than the eventual desired height. Accordingly, the depthmay be between about 1 μm and about 700 μm below the surface on thesubstrate 302. The openings for the TVs 303 may have a diameter ofbetween about 1 μm and about 100 μm. Then the openings for the TVs 303may be filled by a barrier layer and a conductive material, using aprocess such as chemical vapor deposition (CVD) process, plasma enhancedCVD (PECVD), sputtering or metal organic chemical vapor deposition(MOCVD). Excessive barrier layer and excessive conductive materialoutside of the openings for the TVs 303 may be removed through agrinding process such as chemical mechanical polishing (CMP).Afterwards, a thinning of the second side of the substrate 302 may beperformed by a planarization process such as CMP or etching, in order toexpose the openings for the TVs 303 and to form the TVs 303 from theconductive material that extends through the substrate 302. A dielectriclayer 311 may be formed on the substrate 302. The dielectric layer 311may be a representation of a plurality of sub-layers such as inter-metaldielectric layers with various metal layers embedded.

A plurality of contact pads 321 may be formed on the dielectric layer311. Contact pads 321 may be made with aluminum (Al), copper (Cu), tin(Sn), nickel (Ni), gold (Au), silver (Ag), or other electricallyconductive material. The deposition of contact pads 321 uses anelectrolytic plating, sputtering, physical vapor deposition (PVD), orelectroless plating process. The size, shape, and location of thecontact pads 321 are only for illustration purposes and are notlimiting. The plurality of contact pads 321 may be of the same size orof different sizes.

A passivation layer 341 may be formed over the substrate 302, thedielectric layer 311, and above the contact pads 321 for structuralsupport and physical isolation. The passivation layer 341 may be madewith silicon nitride (SiN), silicon dioxide (SiO2), silicon oxynitride(SiON), polyimide (PI), benzocyclobutene (BCB), polybenzoxazole (PBO),or other insulating material. Openings of the passivation layer 341 maybe made by removing a portion of the passivation layer 341 using amask-defined photoresist etching process to expose the contact pads 321.The size, shape, and location of the openings made are only forillustration purposes and are not limiting.

An insulator layer 361, such as a polymer layer 361, may be formed overthe passivation layer 341 and over the passivation layer opening tocover the contact pads 321. An opening of the insulator layer 361 may beformed to expose the contact pads 321. The openings of the insulatorlayer 361 may be made by removing a portion of the insulator layer 361using a mask-defined photoresist etching process to expose the contactpads 321. The size, shape, and location of the opening made are only forillustration purposes and are not limiting.

The RDLs 480 and 489 may be formed above the insulator layer 361. TheRDL 489 may cover the exposed contact pads 321, while the RDL 480 maynot be connected to any contact or conductor within the insulator layers361 or 371. Instead, the RDL 480 acts as a ground plane for thetransmission line 490. While illustrated in FIG. 1( a) as a single layerof dielectric and interconnects, the RDLs 480 and 489 may be formed ofalternating layers of dielectric and conductive material and may beformed through any suitable process (such as deposition, damascene, dualdamascene, etc.). The RDLs 480 and 489 may be made with, e.g., Al, Cu,or a Cu alloy. The RDLs 480 and 489 can be made by an electrolyticplating, sputter, PVD, or electroless plating process. The RDLs 480 and489 can be made with a single layer, or multiple layers using anadhesion layer of Ti, TiW, TaN, Ta or Cr, for example. The device 301may comprise a number of RDL layers to form a network of inter-levelinterconnects according to the function of the semiconductor device.

Another insulator layer 371 may be formed on the RDLs 480 and 489, whichmay be the top layer and surface layer of the device 301. An opening ofthe insulator layer 371 may be formed to expose the RDL 489 while theRDL 480 may be covered by the insulator layer 371. The openings of theinsulator layer 371 may be made by removing a portion of the insulatorlayer 371 using a mask-defined photoresist etching process to expose theRDL 489. The size, shape, and location of the opening made are only forillustration purposes and are not limiting. The insulator layer 371 maybe formed of a polymer, such as an epoxy, polyimide, benzocyclobutene(BCB), polybenzoxazole (PBO), and the like, although other relativelysoft, often organic, dielectric materials can also be used. Formationmethods include spin coating or other commonly used methods. Thethickness of the insulator layer 371 may be between about 5 μm and about30 μm, for example. The dimensions recited throughout the descriptionare merely examples, and will change with the down-scaling of integratedcircuits.

An UBM layer may comprise an UBM pad 391 and an UBM line 390. The UBMpad 391 may be formed around the opening of the insulator layer 371 andconnected to the RDL 489. The UBM line 390 is formed in parallel to theRDL 480, and separated from the RDL 480 by the insulator layer 371. TheUBM pad 391 and UBM line 390 may be formed of copper or copper alloys,which may include silver, chromium, nickel, tin, gold, and combinationsthereof. Additional layers, such as a nickel layer, a lead-freepre-solder layer, or the combinations thereof, may be formed over thecopper layer. The UBM pad 391 and UBM line 390 may have a thickness ofbetween about 1 μm and about 20 μm. The UBM pad 391 may be called acontact pad as well.

The device 301 described above may merely be an example of anembodiment. There may be many other variations different from what isillustrated in FIG. 1( a) and described above. For example, theinsulator layer 361 may not present in some of the embodiments, or theremay be multiple passivation layers 341 in some embodiments. The device301 may have only a RDL contained in an insulator layer.

The die 601 may be packaged with the device 301 through the micro-bumplayer, while the gap between the die 601 and the device 301 is coveredby an underfill 571. The die 601 is connected to the connectors 603,which are placed on the micro-bump 485 within the micro-bump layer.

Connectors 603 may be used to provide connections between the micro-bump485 and the die 601. The connectors 603 may be contact bumps such asmicro-bumps or controlled collapse chip connection (C4) bumps and maycomprise a material such as tin, or other suitable materials, such assilver or copper. In an embodiment in which the connectors 603 are tinsolder bumps, the connectors 603 may be formed by initially forming alayer of tin through any suitable method such as evaporation,electroplating, printing, solder transfer, ball placement, etc., to apreferred thickness of about 100 μm. Once a layer of tin has been formedabove the structure, a reflow may be performed in order to shape thematerial into the desired bump shape.

The underfill 571 may be used between the die 601 and the device 301 tostrengthen the attachment of the die 601 to the device 301 and toprevent the thermal stresses from breaking the connections between thedie 601 and the device 301. Generally, the material for the underfill571, such as organic resin, is selected to control the coefficient ofthermal expansion and the shrinkage of underfill 571. Initially, liquidorganic resin is applied that flows into the gap between the die 601 andthe surface of the device 301, which subsequently cures to control theshrinkage that occurs in underfill during curing.

The micro-bump layer may comprise the micro-bump 485, and the micro-bumpline 470, where the micro-bump 485 is used to connect to other die suchas the die 601, and the micro-bump line 470 is a part of thetransmission line 490. The micro-bump line 470, and the micro-bump 485may be formed at the same time with little or no additional cost, may beof a similar height, and may be made of similar materials. The height ofthe micro-bump layer may be defined by the height of the micro-bump 485,which may depend on the technology used in the package. For example, forcurrent technology, the height of the micro-bump layer may be within therange of about 10 μm to about 50 μm, such as about 27 μm.

The micro-bump 485 may comprise a solder bump 471 formed above a Culayer 475. An optional Ni layer 473 may be in between the solder bump471 and the Cu layer 475. The solder bump 471 may comprise anelectrically conductive solder material, e.g., Sn, Ni, Au, Ag, Cu,bismuthinite (Bi) and alloys thereof, or combinations of otherelectrically conductive material. For example, the solder bump 471 maybe a Cu/SnAg solder bump. The micro-bump 485 may be formed by initiallyforming a Cu layer 475 through methods such as sputtering, evaporation,electroplating, printing, solder transfer, or ball placement, to athickness of, e.g., about 15 μm, followed by forming a Ni layer 473, andfinally followed by forming a solder layer 471 such as lead-free solderSnAg, formed in sequence using the same or similar method for eachlayer. Then a reflow is performed in order to shape the solder layer 471into the desired bump shape shown as the solder bump 471. Any suitablemethod of producing the micro-bump 485 may alternatively be utilized.For example, the micro-bump 485 may be manufactured using the ControlledCollapse Chip Connection New Process (C4NP).

The micro-bump 485 may be placed on an UBM pad 391 of the device 301,sometimes referred to herein as a contact pad. The UBM pad 391 may fillan opening or partially filling an opening of an insulator layer such asan insulator layer 371. The UBM pad 391 may be further connected to ametal layer such as a RDL 489 or a contact pad 321 under the UBM pad 489within the device 301. The micro-bump 485 may be of a height size fromabout 10 μm to about 50 μm. With the continuous reduction of featuresizes and package sizes, the sizes in embodiments may become smallerthan the ones described above. On the other hand, the micro-bump 485 maybe of a bigger size such as a size of a flip-chip bump or a package bumpas well, depending on the particular applications of interest.

The micro-bump line 470 may be made of substantially similar materialsas the materials used for the micro-bump 485. The micro-bump line 470may be placed on the UBM line 390, which is in parallel to the RDL 480.The RDL 480, the micro-bump line 470 separated from the RDL 480 by theinsulator layer 371, and the UBM line 390 under the micro-bump line 470form the transmission line 490, where the RDL 480 is the ground plane,while the micro-bump line 470 and the UBM line 390 form the signaltransmission line.

As illustrated in FIG. 1( a), the micro-bump line 470, which is a partof the signal transmission line, may comprise multiple layers: the layer475 above the UBM line 390 may be a layer of Cu, the layer 473 above thelayer 475 may be a layer of Ni, and the layer 471 above the layer 473may be a layer of lead free solder such as SnAg. On the other hand, themicro-bump line 470 may be of two layers only, the layer 475 above theUBM line 390 may be a layer of Cu, and the layer 471 may be a layer oflead free solder such as SnAg, without the layer 473 of Ni. The layer471 may be a lead free solder layer made of SnAg, with Ag from about 1%to about 2%, and Sn from about 99% to about 98%. The height of the threelayers 471, 473, and 475 may be about the same, or different, which canbe varied according to different requirement. For example, a ratio ofthe heights for the layers 475 of Cu, 473 of Ni, and 471 of lead freesolder may be around 15/1.5/10. The total height of the micro-bump line470 may be within a range from about 10 μm to about 50 μm, e.g., 27 μm.In some alternative embodiments, the signal transmission line 470 andthe ground plane 480 may have a thickness of about 0.5-2 microns.

The micro-bump line 470 may be of a rectangle shape with a width fromaround 10 μm to about 100 μm. The micro-bump line 470 may have a narrow,wide, or tapered shape. The body of the micro-bump line 470 may be of asubstantially constant thickness. The micro-bump line 470 may be ofother shapes such as a circle, an octagon, a rectangle, an elongatedhexagon with two trapezoids on opposite ends of the elongated hexagon,an oval, a diamond, in top views.

In some embodiments, it is desirable for performance of the transmissionline 490 that width of the ground plane line 480 to be about 1.5 timeswidth of signal transmission line, which is the width of the micro-bumpline 470. For better performance, it is further desirable that the widthof the ground plane line 480 to be approximately 2 times width of signaltransmission line 470 in some embodiments. Furthermore, the width isdependent on the distance between the ground plane line 480 and thesignal transmission line 470, which is filled by insulator layer 371, orsome other dielectric layer or substrate. As the distance between theground plane line 480 and the signal transmission line 470 increases,the corresponding width of the signal transmission line 470 increases.In some embodiment, the width of the signal transmission line 470 mayideally be approximately 27.6 microns for a distance between the groundplane line 480 and the signal transmission line 470 of 20 microns.

A simplified view of the package 100 in FIG. 1( a) is shown in FIG. 1(b). As illustrated in FIG. 1( b), the package 100 is formed on a device301. The device 301 comprises a substrate 302, an insulator layer 371 onthe substrate 302, a redistribution layer (RDL) 480 within the device301, and an UBM line 390 on the insulator layer 371. A micro-bump line470 may be formed above the device 301 and in contact with the UBM line390. The RDL 480, the micro-bump line 470 separated from the RDL 480 bythe insulator layer 371, and the UBM line 390 under the micro-bump line470 form the transmission line 490, where the RDL 480 is the groundplane, while the micro-bump line 470 and the UBM line 390 form thesignal transmission line. Alternatively, the RDL 480 may be the signaltransmission line while the micro-bump line 470 and the UBM line 390form the ground plane, as shown in FIG. 1( c). An underfill 571 maycover the micro-bump line 470 and the UBM line 390. There may be a dieplaced above the device 301 and above the underfill 571, connected tomicro-bumps by connectors, which are not shown in FIG. 1( b). Thepackage 100 shown in FIG. 1( b) is a simplified view and there may beother layers within the package 100 not shown. For example, there may bemore layers under the RDL 480, such as copper metal layers with low-Kinter-metal dielectric (IMD) layers, passivation layers, and so on.

Another embodiment of the transmission line 490 is shown in FIG. 1( d)in a similar fashion. As illustrated in FIG. 1( d), the package 100 isformed on a device 301. The device 301 comprises a substrate 302 and aninsulator layer 371 on the substrate 302. The device 301 furthercomprises a first RDL 480 and a second RDL 481 within the insulatorlayer 371 and above the substrate 302. The first RDL 480 and the secondRDL 481 are connected by vias 483. A micro-bump line 470 may be formedabove the device 301. There is no UBM line under the micro-bump line 470in this embodiment. An underfill 571 may cover the micro-bump line 470.There may be a die placed above the device 301 and above the underfill571, connected to micro-bumps by connectors, which are not shown in FIG.1( d). The RDLs 480 and 481 and the micro-bump line 470 separated fromthe RDLs 480 and 481 by the insulator layer 371 form the transmissionline 490, where the RDLs 480 and 481 are the ground plane, while themicro-bump line 470 is the signal transmission line. Alternatively, thesecond RDL 481 may be some other metal layer, instead of a second RDL.For example, there could be a Cu metal layer 481 with a width in a rangefrom about 0.1 um to about 3.5 um, connected to the RDL 480 and formingthe ground plane together, while the micro-bump line 470 is the signaltransmission line. Details of each component of FIG. 1( d) may besubstantially the same as those described for FIG. 1( a).

Another embodiment of the transmission line 490 is shown in FIG. 1( e).As illustrated in FIG. 1( e), the package 100 is formed on a device 301.The device 301 comprises a substrate 302 and an insulator layer 371,where the insulator layer 371 is at a first side of the substrate 302.The device 301 further comprises a RDL 480 at a second side of thesubstrate 302 opposite to the first side. A micro-bump line 470 may beformed above the device 301. The micro-bump line 470 may be in contactwith the insulator layer 371. Alternatively, the micro-bump line 470 maybe above the insulator layer 371 and not in contact with the insulatorlayer 371. There is no UBM line under the micro-bump line 470 in thisembodiment. Alternatively, an UBM line may be formed under themicro-bump line 470. An underfill 571 may cover the micro-bump line 470.There may be a die placed above the device 301 and above the underfill571, connected to micro-bumps by connectors, which are not shown in FIG.1( e). The RDL 480, and the micro-bump line 470 separated from the RDL480 by the insulator layer 371 and the substrate 302 form thetransmission line 490, where the RDL 480 is the ground plane, while themicro-bump line 470 is the signal transmission line. Details of eachcomponent of FIG. 1( e) may be substantially the same as those describedfor FIG. 1( a).

Another embodiment of the transmission line 490 is shown in FIG. 1( f)in a top view. As illustrated in FIG. 1( f), the package 100 may beformed on a substrate 302 which may be a substrate for a device. Aredistribution layer (RDL) 480 may be formed on the substrate 302, andwithin an insulator layer not shown. A micro-bump line 470 may be formedabove the RDL 480. The RDL 480, the micro-bump line 470 separated fromthe RDL 480 by an insulator layer form the transmission line 490, wherethe RDL 480 is the ground plane, while the micro-bump line 470 is thesignal transmission line. The RDL 480 comprises one or a plurality ofopen slots 281, 282, and 283. The open slots 281, 282, and 283 can slowthe wave, and reduce the length needed for the RDL 480 to achievedesired performance. There may be only one open slot, or any othernumber of open slots rather than the three open slots showing in FIG. 1(f). Details of each component of FIG. 1( f) may be substantially thesame as those described for FIG. 1( a).

Microstrip transmission lines shown in FIGS. 1( a)-1(f) are merely onekind of transmission lines. FIGS. 2( a)-2(e) illustrate cross-sectionalviews and a three dimensional view of coplanar waveguide (CPW)transmission lines formed within a package using a micro-bump layer, inaccordance with some additional embodiments. A coplanar waveguide (CPW)transmission line is formed by a signal transmission line separated froma pair of ground planes, all on the same plane, atop a dielectricmedium.

As illustrated in FIGS. 2( a) and 2(b), the package 100 comprising a CPWtransmission line 490 may be formed on a device 301. The device 301comprises a substrate 302 and an insulator layer 371 on the substrate302. There may be other layers of the device 301 not shown, such as thepassivation layer, and contacts. A micro-bump layer comprisingmicro-bump lines 470, 484, and 482 are formed above the device 301. Themicro-bump lines 470, 484, and 482 may be in contact with the insulatorlayer 371. Alternatively, the micro-bump lines 470, 484, and 482 may beabove the insulator layer 371 and not in contact with the insulatorlayer 371. There is no UBM line under the micro-bump line 470 in theembodiment shown in FIG. 2( a). Alternatively, an UBM line 390 may beformed under the micro-bump lines 470, 484, and 482, as shown in FIG. 2(b). An underfill 571 may cover the micro-bump lines 470, 484, and 482.There may be a die placed above the device 301 and above the underfill571, connected to micro-bumps by connectors, which are not shown inFIGS. 2( a) and 2(b).

As shown in FIG. 2( a), the micro-bump lines 470, 484, and 482 form thetransmission line 490, where the micro-bump lines 484 and 482 are a pairof ground planes, while the micro-bump line 470 is the signaltransmission line. As shown in FIG. 2( b), the micro-bump lines 470,484, and 482 and the UBM line 390 connected to each of the micro-bumplines form the transmission line 490, where the micro-bump lines 484 and482 and their connected UBM lines 390 are a pair of ground planes, whilethe micro-bump line 470 and its connected UBM line 390 is the signaltransmission line. The micro-bump lines 470, 484, and 482 are all on thesame plane, atop a dielectric medium such as the insulator layer 371 andseparated by the underfill 571. Details of each component of FIGS. 2(a)-2(b) may be substantially the same as those described for FIG. 1( a).

Alternatively, as shown in FIG. 2( c), for the package 100, someadditional RDL 480 may be formed within the device 301 and connected tothe micro-bump lines 470, 484, and 482 to form the transmission line490. The micro-bump lines 484 and 482 with the connected RDLs 480 are apair of ground planes, while the micro-bump line 470 with the connectedRDL 480 is the signal transmission line. The micro-bump lines 470, 484,and 482 and the connected RDLs 480 are all on the same plane, atop adielectric medium such as the insulator layer 371 and separated by theunderfill 571 and the insulator layer 371. Details of each component ofFIG. 2( c) may be substantially the same as those described for FIGS. 2(a)-2(b) and FIG. 1( a).

Alternatively, as shown in FIG. 2( d), the package 100 further comprisesa second device 601 above the micro-bump lines 470, 484, and 482, andabove the underfill 571. The second device 601 comprises a substrate 302and an insulator layer 371 as well. A RDL 4801 is connected to each ofthe micro-bump lines 470, 484, and 482 in the device 601. A RDL 4802 isconnected to each of the micro-bump lines 470, 484, and 482 in thedevice 301. The transmission line 490 is formed by the RDLs 4801 and4802 together with the micro-bump lines 470, 482, and 484 between thedevices 301 and 601. The micro-bump lines 484 and 482 with the connectedRDLs 4801 and 4802 are a pair of ground planes, while the micro-bumpline 470 with the connected RDLs 4801 and 4802 is the signaltransmission line. The micro-bump lines 470, 484, and 482 and theconnected RDLs 4801 and 4802 are all on the same plane, atop adielectric medium such as an insulator layer 371 and separated by theunderfill 571 and the insulator layer 371. Details of each component ofFIG. 2( d) may be substantially the same as those described for FIGS. 2(a)-2(b) and FIG. 1( a).

The device 301 and device 601 may comprise a substrate 302 and aninsulator layer 371 on the substrate 302. There may be other layers ofthe device 301 and the device 601 not shown, such as the passivationlayer, UBM layer, and contacts. The micro-bump lines 470, 484, and 482are formed above the device 301 as one micro-bump layer. The device 301may be an interposer, a part of a chip or an integrated circuit (IC)die, which may be the back or front side of a die, or a packagesubstrate. Similarly, the device 601 may be an interposer, a part of achip or an integrated circuit (IC) die, which may be the back or frontside of a die, or a package substrate. These devices and any othersuitable devices may alternatively be used and are fully intended to beincluded within the scope of the present embodiments.

Another embodiment of the transmission line 490 is shown in FIG. 2( e)in a three-dimensional view. The transmission line 490 shown in FIG. 2(e) may have the cross sectional view as shown in FIG. 2( d) at somecross section points. The RDLs 4801 may be RDL lines spread out in theinsulator layer of the top device 601 in FIG. 2( d), and the RDLs 4802may be RDL lines spread out in the insulator layer of the bottom device301 in FIG. 2( d). There may be a plurality of micro-bump lines 470,482, and 484 connected to the RDL lines 4801 and 4802. The plurality ofmicro-bump lines 484 and 482 with the connected RDLs 4801 and 4802 are apair of ground planes, while the plurality of micro-bump line 470 withthe connected RDLs 4801 and 4802 are the signal transmission line. Theplurality of micro-bump lines 470, 484, and 482 and the connected RDLs4801 and 4802 are all on the same plane, atop a dielectric medium suchas an insulator layer 371 and separated by the underfill 571 and theinsulator layer 371 as shown in FIG. 2( d).

A variant of CPW transmission line is formed when a ground plane isprovided on the opposite side of the dielectric, which is called afinite ground-plane coplanar waveguide (FGCPW) transmission line, ormore simply, a grounded coplanar waveguide (GCPW) transmission line.FIGS. 3( a)-3(d) illustrate cross-sectional views and a threedimensional view of GCPW transmission lines formed within a packageusing a micro-bump layer, in accordance with some embodiment.

As illustrated in FIG. 3( a), the package 100 comprising a GCPWtransmission line 490 may be formed on a device 301. The device 301comprises a substrate 302 and an insulator layer 371 on the substrate302. A RDL 480 is within the device 301. There may be other layers ofthe device 301 not shown, such as the copper metal layers with low-Kinter-metal dielectric (IMD) layer, passivation layer, UBM layer, andcontacts. A micro-bump layer comprising micro-bump lines 470, 484, and482 are formed above the device 301. The micro-bump lines 470, 484, and482 may be in contact with the insulator layer 371. Alternatively, themicro-bump lines 470, 484, and 482 may be above the insulator layer 371and not in contact with the insulator layer 371. There is no UBM lineunder the micro-bump line 470 in this embodiment. Alternatively, an UBMline may be formed under the micro-bump lines 470, 484, and 482. Anunderfill 571 may cover the micro-bump lines 470, 484, and 482. Theremay be a die placed above the device 301 and above the underfill 571,connected to micro-bumps by connectors, which are not shown in FIG. 3(a).

The micro-bump lines 470, 484, and 482 and the RDL 480 form the GCPWtransmission line 490, where the micro-bump lines 484 and 482 are a pairof ground planes, the RDL 480 is a third ground plane, while themicro-bump line 470 is the signal transmission line. The micro-bumplines 470, 484, and 482 are all on the same plane, atop a dielectricmedium such as the insulator layer 371 and separated by the underfill571. Alternatively, as shown in FIG. 3( b), there may be multiple RDLsegments 480, 482, and 484 formed within the device 301 and a micro-bumpline 470 formed above the device 301, while the RDLs 480, 482, and 484are the signal transmission lines, and the micro-bump line 470 is theground plane. Details of each component of FIGS. 3( a) and 3(b) may besubstantially the same as those described for FIGS. 2( a) and 1(a).

Alternatively, as shown in FIG. 3( c), the ground plane RDL 480 may beconnected by vias 483 to the micro-bump lines 484, and 482, which arealso ground planes, to form the ground plane for the GCPW transmissionline 490. The micro-bump line 470 is still the signal transmission line.The micro-bump lines 470, 484, and 482 are all on the same plane, atop adielectric medium such as the insulator layer 371 and separated by theunderfill 571 and the insulator layer 371. Details of each component ofFIG. 3( c) may be substantially the same as those described for FIGS. 1(a), 2(a), and 3(a).

Alternatively, a three dimensional view of the GCPW transmission line490 of FIG. 3( c) may be shown in FIG. 3( d). The RDL 480 may becontained within the device 301 shown in FIG. 3( c), and connected tothe micro-bump lines 484 and 482 at the micro-bump layer. The RDL 480and the connected micro-bump lines 484 and 482, and the micro-bump line470 separated from the RDL 480 by an insulator layer form the GCPWtransmission line 490, where the RDL 480 and the micro-bump lines 484and 482 are the ground plane, while the micro-bump line 470 is thesignal transmission line. The RDL 480 comprises one or a plurality ofopen slots 281. The open slots 281 can slow the wave, and reduce thelength needed for the RDL 480 to achieve desired performance. There maybe only one open slot, or any other number of open slots rather than thenumber of open slots showing in FIG. 3( d). Details of each component ofFIG. 3( d) may substantially the same as those described for FIGS. 1(a), 2(a), and 3(a).

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps. In addition, each claim constitutesa separate embodiment, and the combination of various claims andembodiments are within the scope of the disclosure.

What is claimed is:
 1. A package, comprising: a device comprising asubstrate, an insulating layer on a first side of the substrate, and afirst redistribution layer (RDL) within the device; a micro-bump layerabove the device, comprising a micro-bump line separated from the firstRDL by the insulating layer; and a transmission line comprising thefirst RDL as a ground plane and the micro-bump line as a signaltransmission line.
 2. The package of claim 1, wherein the signaltransmission line further comprises an under bump metal (UBM) lineplaced above the insulating layer and connected to the micro-bump line.3. The package of claim 1, wherein the micro-bump line comprises a layerof copper and a layer of solder material.
 4. The package of claim 1,wherein the device is an integrated circuit (IC) chip, an interposer, ora package substrate.
 5. The package of claim 1, wherein the ground planefurther comprises a metal layer within the device and connected to thefirst RDL.
 6. The package of claim 1, wherein the first RDL is locatedeither within the insulating layer at the first side of the substrate,or located at a second side of the substrate opposite to the first side.7. The package of claim 1, wherein the first RDL comprises an open slot.8. A package, comprising: a first device comprising a substrate, and aninsulating layer on the substrate; and a micro-bump layer above thefirst device, comprising a first micro-bump line, a second micro-bumpline, and a third micro-bump line, wherein the first micro-bump line andthe second micro-bump line form a pair of ground planes of atransmission line, the third micro-bump line forms a signal transmissionline of the transmission line, and the first micro-bump line, the secondmicro-bump line, and the third micro-bump line are on a same plane, atopthe insulating layer, and separated from each other by an underfillmaterial.
 9. The package of claim 8, wherein the first device furthercomprises a first under bump metal (UBM) line placed above theinsulating layer and connected to the first micro-bump line, a secondUBM line placed above the insulating layer and connected to the secondmicro-bump line, and a third UBM line placed above the insulating layerand connected to the third micro-bump line.
 10. The package of claim 8,wherein the first micro-bump line comprises a layer of copper and alayer of solder material, the second micro-bump line comprises a layerof copper and a layer of solder material, and the third micro-bump linecomprises a layer of copper and a layer of solder material.
 11. Thepackage of claim 8, wherein the first device is an integrated circuit(IC) chip, an interposer, or a package substrate.
 12. The package ofclaim 8, wherein the first device further comprises a firstredistribution layer (RDL) within the first device connected to thefirst micro-bump line, a second RDL within the first device connected tothe second micro-bump line, and a third RDL within the first deviceconnected to the third micro-bump line.
 13. The package of claim 12,further comprising: a second device above the micro-bump layer,comprising a fourth RDL within the second device and connected to thefirst micro-bump line, a fifth RDL within the second device andconnected to the second micro-bump line, and a sixth RDL within thesecond device and connected to the third micro-bump line.
 14. Thepackage of claim 13, further comprising: a fourth micro-bump lineconnected to the first RDL and the fourth RDL, a fifth micro-bump lineconnected to the second RDL and the fifth RDL, and a sixth micro-bumpline connected to the third RDL and the sixth RDL.
 15. The package ofclaim 8, further comprising: a seventh RDL within the first device,which is a third ground plane of the transmission line.
 16. The packageof claim 15, wherein the seventh RDL is connected to the firstmicro-bump line and the second micro-bump line.
 17. The package of claim15, wherein the seventh RDL comprises an open slot.
 18. A method forforming a transmission line, comprising: providing a device comprising asubstrate, an insulating layer on a first side of the substrate, and afirst redistribution layer (RDL) within the device, wherein the firstRDL is a ground plane of the transmission line; forming a firstmicro-bump line above the device, separated from the first RDL by theinsulating layer, wherein the first micro-bump line is a signaltransmission line of the transmission line; and covering the firstmicro-bump line with an insulating underfill material.
 19. The method ofclaim 18, wherein the first RDL is located either within the insulatinglayer at the first side of the substrate, or located at a second side ofthe substrate opposite to the first side.
 20. The method of claim 18,further comprising: forming a second micro-bump line and a thirdmicro-bump line above the device as a pair of ground planes for thetransmission line, and the first micro-bump line, the second micro-bumpline, and the third micro-bump line are on a same plane, atop theinsulating layer, and separated from each other by the underfillmaterial.